At the club I train at, 'sensei' is used more-or-less a gesture of politeness and respect acknowledging the training and knowledge acquired by a person. We don't usually use the term off-the-mat, but do sometimes. Generally a person starts being called sensei when they reach shodan as they usually begin to take on teaching responsibilities. I don't think the grade matters particularly with the term - I see it simply as an acknowledgement that the person being referred to is a person from whom others can learn.
Last edited by miser : 09-10-2012 at 11:14 AM.